Synthetic surfaces that are resistant to fouling by aqueous media, organic fluids, or biological organisms are critical in a broad range of industrial, commercial, and biomedical contexts. Surfaces that are superhydrophobic, superoleophobic, or superomniphobic, for example, form a basis for the design of self-cleaning and antifogging materials, anti-corrosive interfaces, and stain-resistant textiles, and have enabled new strategies for the transport and manipulation of complex fluids, including approaches to oil recovery and oil/water separation (see Liu et al., Chem. Soc. Rev. 2010, 39, 3240; Banerjee et al., Adv. Mater. 2011, 23, 690; Yao et al., Adv. Mater. 2011, 23, 719; Liu et al., Ann. Rev. Mater. Res. 2012, 42, 231; Campoccia et al., Biomaterials 2013, 34, 8533; Ueda et al., Adv. Mater. 2013, 25, 1234; Bellanger et al., Chem. Rev. 2014, 114, 2694; Genzer et al., Science 2000, 290, 2130; Tuteja et al., Science 2007, 318, 1618; Chu et al., Chem. Soc. Rev. 2014, 43, 2784; and Deng et al., Science 2012, 335, 67).
Slippery liquid-infused porous surfaces (SLIPS) are an emerging class of synthetic materials that exhibit unique and robust antifouling behavior. These materials are fabricated by infusion of viscous oils into porous surfaces, yielding interfaces that allow other fluids to slide off with sliding angles sometimes as low as 2°. This slippery behavior arises from an ability to host and maintain thin films of oil at their surfaces, placing a premium on chemical compatibility between the matrix and the oil and revealing design criteria that can be exploited to manipulate the behaviors of contacting fluids (e.g., to tune sliding angles and velocities or create responsive surfaces that allow control over these and other interfacial behaviors). Surfaces and coatings that exhibit these characteristics have enabled the design of new anti-icing surfaces, slippery containers for the dispensing of commercial liquids and gels, and new liquid-infused interfaces that are resistant to biofouling in complex aqueous, biological, and marine environments.
Recent reports on alternative approaches to the development of SLIPS have enabled the design of new classes of synthetic and highly ‘slippery’ anti-fouling materials that address practical limitations exhibited by conventional non-wetting (e.g., superhydrophobic) surfaces, and introduce new principles for the design of robust, injury-tolerant, and mechanically compliant synthetic anti-fouling surfaces (see Wong et al., Nature 2011, 477, 443; Grinthal et al., Chem. Mater. 2014, 26, 698; Epstein et al., Proc. Natl. Acad. Sci. U.S.A. 2012, 109, 13182; Yao et al., Nat. Mater. 2013, 12, 529; Liu et al., Adv. Mater. 2013, 25, 4477; Smith et al., Soft Matter 2013, 9, 1772; Vogel et al., Nat. Commun. 2013, 4; Huang et al., ACS Macro Lett. 2013, 2, 826; Leslie et al., Nat. Biotechnol. 2014, 32, 1134; Glavan et al., Adv. Funct. Mater. 2014, 24, 60; Wei et al., Adv. Mater. 2014, 26, 7358; Yao et al., Adv. Mater. 2014, 26, 1895; and Zhang et al., Adv. Funct. Mater. 2014, 24, 1074.)
Reports by Aizenberg, Levkin, and others demonstrate that SLIPS can be designed to resist fouling by bacteria and other marine organisms that can colonize and form biofilms on biomedical devices or commercial and industrial equipment (see Epstein et al., Proc. Natl. Acad. Sci. U.S.A. 2012, 109, 13182; Leslie et al., Nat. Biotechnol. 2014, 32, 1134; Howell et al., ACS Appl. Mater. Inter. 2014, 6, 13299; Li et al., ACS Appl. Mater. Inter. 2013, 5, 6704; and Xiao et al., ACS Appl. Mater. Inter. 2013, 5, 10074). Those studies suggest that appropriately designed liquid-infused surfaces can resist the attachment, colonization, and organization of communities of these organisms in ways that exceed those exhibited by some conventional anti-fouling surfaces (such as surfaces modified with polyethylene glycol and non-wetting superhydrophobic surfaces, etc.), even in complex media with proteins, surfactants, or at high ionic strengths typical of environmental conditions encountered in many applied and biologically relevant contexts.
While these past studies represent outstanding progress toward the design of new anti-fouling materials with superior functional properties, existing SLIPS do not completely inhibit colonization, and fundamental questions remain regarding both the long-term stabilities of these materials and the ability of bacteria or other microorganisms to adapt to or breach the infused liquid barriers that confer slippery character to establish ‘beachheads’ on underlying surfaces that could enable colonization and bio-fouling. In addition, and of particular interest in the context of potential biomedical applications of these new materials, SLIPS can currently do little to influence the behaviors of planktonic microorganisms—that is, while SLIPS can substantially prevent the adhesion of pathogenic microorganisms or the formation of microbial biofilms on treated surfaces, they cannot prevent the growth or proliferation of those organisms in solution, prevent them from colonizing other nearby surfaces, or stop them from engaging in other behaviors (e.g., toxin production) that could lead to infection and other associated burdens.
The present invention addresses these issues and allows for the functional properties and potential applications of SLIPS to be significantly expanded by adopting design strategies that leverage the potential of the porous matrices and the infused and lubricating oils in these materials as depots for the storage and subsequent release of bioactive agents. In particular, small-molecule anti-microbial agents can be stored in the porous matrices or dissolved and stored in a fugitive oil phase without compromising the ‘slippery’ characteristic of the material, thereby providing new approaches to the design of multi-functional or dual-action SLIPS with improved antimicrobial properties. Provided that the embedded agent can also diffuse into the oil phase and/or from the oil phase into surrounding aqueous media, this approach also offers opportunities to design anti-fouling SLIPS that could kill or influence the behaviors of planktonic microorganisms. In a broader and more general context, the ability to store and control the release of small molecules or other agents from SLIPS allows for a wide range of other new applications for these liquid-infused materials.